sourdough

Short definition from Wiktionary

Noun

1. 1
   A type of bread dough leavened with yeast and lactobacilli that produce acids giving a sour taste.
2. 2
   An old-timer, especially in Alaska.
3. 3
   A permanent resident of the territory. Someone who has lived in the Yukon during all four seasons.
4. 4
   A 49er, a California Gold Rush miner.
5. 5
   Leaven; an agent that makes dough rise.